This invention relates to methods of and apparatus for winding a wire around a toroidal core, and more particularly it is concerned with a method of and an apparatus for forming a coil suitable for winding a wire around a very small toroidal core used with a magnetic head of a computer or videotape recorder.
An apparatus disclosed in U.S. Pat. No. 4,184,644 is known for producing a coil on a toroidal core. This coil winding apparatus includes a traveling ring and a shuttle arranged in a right-angle relation to the toroidal core, the shuttle having a wire of a predetermined length wound thereon and the toroidal core having one end of the wire secured thereto, the traveling ring and the shuttle being rotated to thereby wind the wire around the toroidal core to form a coil.
This apparatus has the disadvantage that it can not be utilized with toroidal cores of the type that are too small for the traveling ring and the shuttle to be introduced into the inner region of the toroidal core.
As an apparatus for mechanically winding a wire around a toroidal core which is too small for a coil thereon by using a traveling ring and a shuttle, a winding apparatus as disclosed in Japanese Patent Publication No. 3171/63 is known which effects winding of a wire around a toroidal core by manipulating a needle connected to one end of a wire to be wound around the toroidal core.
More specifically, the winding apparatus comprises a chuck for gripping the needle connected to one end of the wire, a hammer located above the toroidal core held in the winding position by support means, a support table, interposed between the toroidal core and the hammer, formed with an opening for the needle to extend therethrough and a groove for the wire to be pulled therethrough, and a pair of rollers located below the toroidal core for rotational and sliding movements.
The wire of a predetermined length is passed through the eye of the needle at one end thereof and connected thereto, and then the other end of the wire is secured to the toroidal core. Thereafter the needle is gripped by the chuck which is positioned above the opening formed in the support table. The hammer is moved downwardly to press the needle gripped by the chuck downwardly, to let the forward end of the needle extend through the opening of the support table and the toroidal core and emerge from the toroidal core at its lower portion. Simultaneously as the chuck is opened to release the needle, the chuck is moved to a position below the toroidal core to grip the needle again. Then the needle is moved downwardly and withdrawn from the toroidal core, and moved to a position below the rollers. As the needle passes between the pair of rollers, the rollers rotate while being brought into engagement with each other to hold the wire therebetween, to thereby withdraw the wire from the toroidal core. At this time, the wire clears the groove of the support table to be wound around the toroidal core. Meanwhile, the chuck moves the needle to a position between the support table and the hammer in which the forward end of the needle is positioned against the opening of the support table. Upon completion of withdrawing of the wire, the rollers are brought out of engagement with each other, to release the wire.
By repeating the process described hereinabove, the wire of a predetermined length can be wound around the toroidal core to form a coil.
In the coil winding apparatus described hereinabove, difficulties are experienced in winding a wire around a toroidal core of the small size, such as the one used in a magnetic head of a computer or viedo tape recorder, in which a wire of 0.03 mm in diameter is wound around two widthwise separated sections of a toroidal core of a length of 3 mm, a width of 2.3 mm and a thickness of 0.15 mm formed in its central portion with an opening of a length of 0.45 mm and a width of 0.3 mm.
When a wire is wound around the toroidal core of the aforesaid dimensions, the opening of the toroidal core would have a width of about 0.1-0.15 mm due to the presence in the opening of the wire and to a bulge caused by the rigidity of the wire upon completion of winding. Meanwhile the needle of the winding apparatus is required to have a diameter of at least 0.2-0.3 mm when the strength of the needle and other factors are taken into consideration, and preferably the diameter is over 0.5 mm. Thus unless the opening of the toroidal core has a dimension of over 0.3 mm when the wire is wound thereon, the coil already produced on the toroidal core or the edge of the opening of the toroidal core would be damaged by the needle and the wire introduced into the opening by the needle.
The finer the wire, the lower is its rigidity. The wire of reduced rigidity might be bent between the underside of the toroidal core and the eye of the needle, so that the wire might catch against the support table and be rounded to produce a kink. When this phenomenon occurs, further continuation of the winding operation would become impossible.
In view of the status of the art of winding a wire around a toroidal core that prevails nowadays as described hereinabove, highly skilled techniques of the workers are relied on in manually winding a wire around a very small toroidal core, with very low operation efficiency.